Agar/Agarose Oligosaccharides

Agar is not one substance. Hot water pulls a family of galactans out of the algal cell wall, and that extract splits into two very different halves: agarose, the neutral linear polymer that does the gelling, and agaropectin, the charged, sulfated fraction that mostly gets in the way. Their ratio is set before the kettle is even switched on — by species, by harvest season, and by whether the biomass saw an alkaline pretreatment. Everything downstream, from gel strength to the background on a stained slab, traces back to that split.

What makes agarose worth working with is its hysteresis. It melts near 88 °C and only sets again around 36 °C. That wide separation gives you a window of roughly fifty degrees in which the solution is still liquid but no longer hot, which is the whole reason it can be poured, seeded with something heat-sensitive, and then left to set quietly. Our range covers the powder grades that go into that window, the cross-linked bead matrices built from the same polymer, and oligosaccharide fractions cut from it at a stated chain length.

Two genera carry the trade, and they do not behave alike

Gelidium and Pterocladia yield relatively little agar but deliver the strongest gels and the narrowest thermal window. Gracilaria gives far more volume, and after a dilute alkali pretreatment at 1–2% NaOH — which strips sulfate groups off the agaropectin — its gel strength climbs into the same territory. Because a specification can be met from either direction, we quote the agarophyte alongside the numbers rather than instead of them.

The figures above are for 1% gels and follow the established agarophyte groupings: the Gelidium group gives the highest strength and the widest thermal gap, while Gracilaria is quoted both before and after alkali modification because the treatment changes the answer. Yield, gel strength and even gelling temperature move with species, harvest season and extraction conditions, so we treat them as a starting point for a specification rather than as constants.

The same polymer, six ways

Six numbers decide whether the gel will behave

A gel strength figure quoted on its own is close to meaningless, because it always travels with a concentration and a temperature. Agarose measured at 1% and at 1.5% gives two different numbers, and gelling points drift with the ionic content of the buffer you dissolve it in. When you compare two suppliers, compare the concentration, the temperature and the method as well as the value.

Hysteresis is the feature, not an artefact

Agarose sets by cooling, not by reacting. That single fact separates it from gelatin and from the carrageenans, whose working windows are far narrower. The published figures for the agar extracted from Gelidium show a gap of roughly fifty-one to sixty degrees; Gracilaria agars can run anywhere from twenty-three to fifty-nine degrees depending on the methoxyl content, and a higher methoxyl content pushes the gelling temperature upward. If your protocol depends on pouring a gel and then holding it, that gap is the property you are buying.

Two families, separated by which bond the enzyme chooses

Hydrolysing agarose does not simply shorten the chain — it produces two chemically distinct series, depending on which of the two alternating linkages is cut. Acid or an α-agarase attacks the α-(1→3) bond and gives agaro-oligosaccharides that repeat as agarobiose, with 3,6-anhydro-L-galactose at the reducing end. A β-agarase, the enzyme most agar-degrading marine bacteria produce, cuts the β-(1→4) bond instead and gives neoagaro-oligosaccharides that repeat as neoagarobiose, with D-galactose at the reducing end. Both series contain the same two sugars, so a mass figure alone will not tell you which one you have.

The conditions are not interchangeable either. A published preparation using β-agarase from Vibrio natriegens ran at 45 °C and pH 8.5 with a 0.3% substrate load and 100 U of enzyme per gram, held for twenty hours, after which pigment was stripped on activated carbon, salts were dialysed out and the mixture was fractionated on a Bio-Gel P2 column. That sequence — enzyme, decolourise, desalt, separate — is what turns a hydrolysed syrup into a defined fraction, and it is the part of the process we keep under our own control rather than buying in.

What we can separate, and what each cut is for

Because the two series are built from the same two monosaccharides, a fraction at a given degree of polymerisation carries the same mass whichever route produced it: each agarobiose repeat adds approximately 324 Da, which places a DP 6 cut close to 972 Da and a DP 12 cut near 1 944 Da. A molecular weight therefore narrows the possibilities but does not settle them. That is why the linkage and the identity of the reducing end belong on the certificate alongside the chain length.

A DP figure is only as good as the method behind it

Chain length is easy to claim and harder to demonstrate. The published high-performance anion-exchange systems resolve neoagaro-oligosaccharides to DP 46 and agaro-oligosaccharides to DP 32 with pulsed amperometric detection, and size-exclusion separation has been used to isolate individual cuts across DP 2–22. If a fraction arrives without the method stated, the number on the label cannot be compared with anyone else's.

Cross-linked beads, and why the percentage comes first

Agarose is neutral and biologically inert as a matrix, which is exactly why it needs a ligand before it will select anything. Cross-linking is the other half of the story: it raises pressure stability so the matrix can be run at flow rates that would compress an uncross-linked gel, and it also tightens the pore structure. The practical rule is that a higher agarose concentration gives smaller pores and a lower exclusion limit.

Ligands are what we couple onto whichever matrix you choose. Affinity routes cover nickel-NTA for histidine-tagged targets, glutathione for GST fusions, Protein A and Protein G for antibodies, and streptavidin for biotinylated material. Ion-exchange routes cover the weak anion exchanger DEAE, the strong anion quaternary amine, and the weak and strong cation exchangers CM and sulfopropyl. We also supply the base matrix pre-activated — glyoxal, NHS or epoxy — for groups who prefer to attach their own ligand, and plain, underivatised beads for size-exclusion separations.

Slab, bead, solution or powder

What keeps a batch usable after it is opened

– Powdered agarose takes up moisture. Keep containers closed, at room temperature, in low humidity, and bring a cold container back to room temperature before opening it so condensation does not land on the powder.

– Dissolve by heating with vigorous stirring rather than by adding powder to already-boiling liquid; unmixed powder scorches onto the vessel and that fraction never goes into solution.

– Because gel strength depends on the final concentration, weigh with the moisture figure in mind when you are comparing one lot against another.

– Repeated melting and cooling degrades the gel. Cast what you need and discard the rest rather than re-using a slab.

– Oligosaccharide fractions are hygroscopic and light-sensitive. Store them sealed and dry, protect them from light, and do not leave a vial open on the bench during weighing.

– Cross-linked beads must never be allowed to dry out or to freeze. Keep them in buffer with a preservative, and handle them gently to avoid fracturing the bead population.

What stays the same from lot to lot

– Gel strength is always measured at a stated concentration and a stated temperature, and the method travels with the value.

– EEO and sulfate content are reported per lot, since they move together and both affect band sharpness.

– Gelling and melting temperatures are quoted as ranges rather than as single figures, because that is what the measurement actually gives.

– Nuclease testing is carried out on every lot, not on a representative sample from the production run.

– Each oligosaccharide fraction is checked against the same reference ladder, so a DP 6 from this year matches a DP 6 from last year.

– The alkaline pretreatment step is recorded and traceable, so the extent of agaropectin removal can be reproduced rather than guessed.

– A retained sample is kept from every lot for comparison against future production.

Tell us the constraint, and we adjust the line

Most of what leaves our facility is not a catalogue item. It is a standard grade with one or two variables moved, and the fastest route to it is a description of what is going wrong rather than a product code.

If the problem is a gelling time, a resolution or a bead size rather than a part number, describe it in those terms. A supplier who only quotes a number cannot help you move a method that is nearly working, and that is the conversation worth having first.

For Research or Industrial Raw Materials, Not For Personal Medical Use!